1. Field of the Invention
The present invention relates to an electrode system, to be implanted in a heart and connected with a proximal end to a medical apparatus for monitoring, diagnosing and/or treating a heart, of the type having an electrode lead, an atrial electrode arranged on the electrode lead for electrical connection to tissue in an atrium of the heart, and a first electrode conductor arranged in the electrode lead for connecting the atrial electrode to a first contact at the proximal end.
The present invention also relates to an electrode system of the above type which further has a ventricular electrode, arranged on the electrode lead, for electrical connection to tissue in a ventricle of the heart and a second electrode conductor, arranged in the electrode lead, for connecting the ventricular electrode to a second contact at the proximal end.
2. Description of the Prior Art
The implantation of electrode systems for medical purposes in children poses a problem for conventional electrode systems. The electrode lead between the medical apparatus and heart must stretch as the child grows and thus damages tissue in the patient's body. To prevent this damage, a surplus length of electrode lead is sometimes implanted in a loop around the medical apparatus to serve as additional lead length during the child's growth. Utilizing this additional lead length, however, requires surgery to unwind the surplus length and to introduce the necessary additional length of electrode lead into a vein towards the heart.
Another problem with conventional electrode systems is the need for a plurality of electrode leads for different uses, e.g., when both the ventricle and the atrium are to be stimulated or sensed (as in DDD-systems), when the atrium is to be stimulated and a physiological parameter is to be sensed.
A large number of physiological parameters related to the heart's function is known. In addition to the electrical signals from the heart, blood pressure, blood flow, oxygen saturation, pH, blood temperature etc., are parameters of interest. A number of these parameters can advantageously be measured in the ventricle, so two electrode leads are required when the atrium is to be stimulated and a physiological parameter is to be sensed in the ventricle.
Yet another problem occurs with conventional electrode systems utilizing defibrillation electrodes to be placed in the heart for defibrillating the atrium, the ventricle or both. In particular the atrial defibrillation electrode is difficult to arrange in a steady position within the atrium.
For heart stimulators in which both the atrium and ventricle are to be stimulated and/or electrically sensed, a number of electrode systems has been devised to facilitate implantation and, primarily, to reduce the number of electrode leads which have to be implanted in the heart.
One such electrode system is described in U.S. Pat. No. 4,567,901. This electrode system has a common electrode lead which divides inside the heart into an atrial electrode lead and a ventricular electrode lead. Even if this electrode system can be manipulated into the heart during implantation, the atrial electrode and the ventricular electrode must still be positioned and affixed as if they were arranged on separate electrode leads.
Another known electrode system is described in U.S. Pat. No. 4,444,195. This electrode system has a single electrode lead with one or a plurality of ventricular electrodes at the distal end of the electrode lead and one or a plurality of atrial electrodes arranged at an appropriate distance from the distal end. The electrode lead has a slight curvature between the ventricular electrodes and the atrial electrodes causing the latter to contact atrial tissue. One problem with this type of electrode system is that the electrical contact between the atrial electrodes and atrial tissue cannot be assured. It can, therefore, only be employed in VDD-systems and not in DDD-systems.
A similar electrode system is described in U.S. Pat. No. 4,154,247. The electrode lead in this electrode system is devised with more geometric variations at the atrial electrode. For example, the electrode lead in one embodiment is laid in a circle to enable the atrial electrode to establish continuous electrical contact with atrial tissue. In another embodiment, the electrode lead is S-shaped at the atrial electrode. Essentially the same problems occur with this electrode system. It cannot, therefore, be employed in a full range DDD-system.